Charlot, jr
electrical detecting means

ABSTRACT

AN ELECTRICAL DETECTING APPARATUS UTILIZING A FREQUENCY SHIFTING OSCILLATOR FOR GENERATING A RADIO FREQUENCY SIGNAL WHICH IS TRANSMITTED BY A RADIATING MEANS IN A PROPAGATED WAVE AND INTERCEPTED BY A TARGET RESULTING IN A REFLECTED WAVE WHICH IS DETECTED BY A RECEIVING MEANS WHEREIN THE RECEIVED REFLECTED WAVE IS USED TO SHIFT THE OSCILLATOR OPERATING FREQUENCY FOR INDICATING TARGET DETECTION BY A DOPPLER FREQUENCY SHIFT IS SHOWN.

l..- H. CHAIRLOT. JR Re. 27,064

Feb. 16, 1971 ELECTRICAL DETECTING MEANS Original Filed Feb. 17. 1967 25Sheets-Sheet Fl 6 kM07Z-' l 6 RECEIVER V40 i/42 /44 i (Mr) a 3 I m h frv 71015 Q- k 75 A INVENTOR.

V We zgvcauv/ilmwzJe 4 TOR/V575 TIME L. H. CHARLOT, JR Re. 27,064ELECTRICAL DETECTING, "BANS Original Filed Feb. 17. 1967 Feb. 16, 1971 3Sheets-Sheet 3 ANTENNA :m 767-! 0 M 9 Z '7: v I Vi: Q m.

V VfLOC/TY a M R n g M 77 -mr m m m K V 4 0/. E mam m M we a 6 F a N a u4 a P a M I. 4 a R m s 0 E r R w n w n w w W |||l|l| 6 0 R J M a 7, 0 mL Y N R E A W H w w. m Um v WT w A MI W .Qiumbwuaq TIME (t) UnitedStates Patent Office Re. 27,064 Reissued Feb. 16, 1971 27,064 ELECTRICALDETECTING MEANS Lincoln H. Chariot, Jr., Tampa, Fla., assignor toMinnesota Mining 8: Manufacturing Company, St. Paul, Minn., acorporation of Delaware Original No. 3,407,403, dated Oct. 22, 1968,Ser. No. 616,924, Feb. 17, 1967. Application for reissue July 24, 1969,Ser. No. 853,560

Int. Cl. G01s 9/42 US. Cl. 343- 16 Clalms Matter enclosed in heavybrackets [II appears In the original patent but forms no part of thisreissue specification; matter prlnted In ltallcs Indicates the additionsmade by reissue.

ABSTRACT OF THE DISCLOSURE An electrical detecting apparatus utilizing afrequency shifting oscillator for generating a radio frequency signalwhich is transmitted by a radiating means in a propagated wave andintercepted by a target resulting in a reflected wave'which is detectedby a receiving means wherein the received reflected wave is used toshift the oscillator operating frequency for indicating target detectionby a Doppler frequency shift is shown.

Use of electrical detecting apparatus for sensing moving objects isknown. Certain types of known detectors, such as the devices of PatentsNos. 3,210,752 and 3,242,- 486, employ an oscillator which establishes afixed operating frequency for the detector oscillator. Such detectorssense the presence of a moving object by use of antennas which transmita continuous wave radio frequency signal.

In Patent No. 3,210,752, for example, the moving object interrupts thefield and causes reflected waves to be directed back to the same antennatransmitting the radio frequency signal whereby a detected signal havingan amplitude which is a function of the reflected wave is produced. Theamplitude and phase of the transmitted radio frequency signal arecompared to the amplitude and phase of the detected signal and thedifference therebetween is utilized directly as a means for detectingthe presence of a moving object.

In Patent No. 3,242,486, for example, a radio signal having a fixedfrequency is radiated as acontinuous wave in a preselected area. Amoving object intercepts the continuous wave and causes a portion of thecontinuous wave to be directed back to a separate antenna and detectingcircuit. The detecting circuit also has a part of the radio signal at afixed frequency applied thereto from the radiating means. The detectingcircuit mixes the fixed frequency signal with the received signal andproduces an output signal which changes as a function of the differencebetween the radiated and received frequency, which frequency is theDoppler frequency. Additionally, the amplitude of the Doppler frequencysignal varies directly in proportion to the amplitude of the receivedsignal. After the Doppler frequency signal (which is in the kilocyclerange) is generated, it is applied to a discriminating circuit whichactuates an alarm device if the amplitude of the Doppler frequencysignal exceeds a predetermined level.

In these types of devices, it is essential that a stable oscillator beused in that the output signal has a fixed amplitude, phase andfrequency. Further, electrical sensing apparatuses of the prior art arenot self-detecting in that the operational characteristics of thecircuit do not change and an external detector is necessary to detectthe moving object.

Another type of electrical detecting apparatus, disclosed in Patent No.3,201,774, utilizes an oscillator having a tank circuit under control ofa feedback circuit having an additional resonant circuit. The additionalresonant circuit controls the state of the oscillator, viz, whether theoscillator is in oscillation or disabled. The oscillator frequency isdetermined by the tank circuit and the pick-up device is either thecapacitance or inductance component of the resonant circuit.

The electrical detecting means of the present invention provides asubstantial improvement over the prior art devices. The improvementresides in a sensitive electrical sensing apparatus which is responsiveto a feedback signal which varies in phase, which'may or may not be atime related variance, to change the operating frequency of anoscillator as a function of target detection.

In one embodiment of the present invention, an oscillator having aresonant circuit produces a radio frequency signal at the frequency ofthe resonant circuit when a feedback signal having a predetermined phasegenerated with- I in a feedback network, is applied to the oscillator.The radio frequency signal, at this resonant frequency, is trans mittedby a first antenna into an area or space to be monitored. A propagatedwave is established having a radiation pattern which depends on theenvironmental conditions of the monitored spaced and characteristics ofthe first antenna. A second antenna, which is electrically coupled tothe feedback network, receives reflected waves, the phase and magnitudeof which are dependent upon the environmental conditions in a mannersimilar to the first antenna. When a target enters the space monitoredby the electrical detecting means, the target intercepts the propagatedwave radiation pattern causing a reflected wave which is received by thesecond antenna.

The second antenna, in response to the reflected wave, applies a signalrepresentative of the reflected wave to the feedback network. Thefeedback network produces a feedback signal having a new phase which isdetermined by the reflected wave sensed by the second antenna. Thefeedback signal, having a new phase, is combined with or interacts withan internally derived feedback signal generated by the feedback network.A feedback signal having a phase which is a function of the sensedreflected wave is applied to the oscillator causing the oscillator tochange its operating frequency. The new frequency of the oscillator isretransmitted by the first antenna establishing a new propagated wavewherein' the frequency of the radio frequency signal is changed. Bymeasuring the operating frequency shifts of the oscillator with respectto time, an

output signal is generated as a function of the Doppler frequency shiftattributed to the intercepting target. By means of output samplingdevices, an output signal can be produced which is a function of targetvelocity.

The electrical detecting means of the present invention can be utilizedin a pulse controlled radar system for tracking a moving target wherebytarget velocity and range can be very accurately computedrSuch a radarsystem ;tilizes the frequency shifts of the oscillator for deteiminingthe target velocity. The Doppler effect of the reflected wave isinternally derived as the target moves relative to the radar systemantenna and a vectored target velocity representation is provided. Thetarget reflected wave is received by a receiving antenna and amplifiedby a radio frequency signal amplifier. The amplified received signal isapplied to a feedback network which ultimately varies the oscillatoroperating frequency thereby indicating target velocity.

The range or distance of the target is determined by the time intervalbetween transmission of a pulse of radio frequency signal by the antennaand of a reflected pulse from a target received by the antenna.

This radar system provides a substantial improvement over the knownradar systems. Known radar systems require expensive and bulkyl delaylines. A pulse controlled radar system based on the teachings of thisinvention provides a relatively simple and reliable system for trackingmoving targets such as, for example, a high speed aircraft or a spacecapsule;

One advantage of the present invention is to provide an electricaldetecting means which indicates detection of an intruding target byshifting the operating frequency of an oscillator.

Another advantage of the present invention is that the velocity of amoving detected target can be determined by incremental changes inoscillator frequency and power.

A further advantage of the electrical detecting apparatus of thisinvention is that a target capable of producing a reflected radiofrequency signal wave can be detected.

An additional advantage of the present invention is that an inexpensive,portable, completely enclosed, single transistor electrical detectingapparatus for sensing presence of an intruding target can be constructedwherein the output signal thereof can be picked up by a remote receivertuned to the frequency of the detector oscillator.

Yet another advantage of the present invention is-that the electricaldetecting means can be adapted for use in a pulse controlled radarsystem for tracking'a target in space.

The above and further advantages of this invention will be apparent fromthe following description of a preferred embodiment and other alternateembodiments with reference to the accompanying drawing wherein:

FIGURE 1 is a block diagram illustrating the elcc trical detecting meansof the present invention;

FIGURE 2 is a graph illustrating the frequency deviations of anoscillator, within the electrical detecting means of FIGURE 1, as afunction of target distance from a receiving antenna;

FIGURE 3 is a graph illustrating the relationship between input powerand frequency for an oscillator utilized in the electrical detectingmeans of FIGURE 1;

FIGURE 4 is a schematic diagram-illustrating one embodiment of thepresent invention utilizing a single transistor oscillator-detectorconnected in a common base configuration;

FIGURE 5 is a schematic diagram illustrating another embodiment of thepresent invention utilizing a single transistor oscillator-detectorconnected in a commonemitter configuration;

FIGURE 6 is a schematic diagram of yet another embodiment of the presentinvention having an output sampling means for producing an output signalhaving pulse period modulation;

FIGURES 7A and 7B are graphs illustrating waveforms at two terminalpoints in the embodiment of FIGURE 6;

FIGURE 8 is a block diagram of a pulse controlled radar system utilizingthe present invention; and

FIGURE 9 is a graph illustrating a waveform of the output signal fromthe pulse controlled radar system of FIGURE 8.

Briefly, the electrical detecting means of the present invcntioncomprises means including reasonant means for producing a radiofrequency signal at a resonant frequency in response to a feedbacksignal having a predetermined phase. When the phase of the feedbacksignal is shifted to a phase other than the predetermined phase, theproducing means produces a radio frequency signal at a frequency off theresonant frequency. The radio frequency signal produced by the producingmeans is radiated by radiating means in a propagated wave. Prior to atarget intercepting the propagated wave, the feedback means establishesa feedback signal having a first phase to opcrate the producing means ata first frequency. When a target intercepts the propagated wave. thereflected wave is sensed by a receiving means and the receiving meansapplies a signal which is a function of the reflected wave.

4 to a feedbackmeans. The feedback means changes the phase of thefeedback signal to a phase other than the first phase to shift thefrequency of the producing means from a first frequency to a secondfrequency in response to the receiving means detecting a reflected wavefrom the target intercepting the propagated wave.

Referring now to the block diagram of FIGURE 1, the electrical detectingmeans of the present invention includes a means including resonant meansfor producing a radio frequency signal at a resonant frequency, or anoscillator 10. In one embodiment, oscillator :10 includes an amplifier12 and a resonant means 14 and an internal feedback means 16. Resonantmeans 14 and internal feedback means 16 are shown connected in series toillustrate the functional efi'ect resonant means 14 has on feedbackmeans 16, specifically, to illustrate that means 16 provides feedbackthroughout a band centered about the resonant frequency of means 14. Anexternal feedback means 18 having means for radiating a radio frequencysignal in a propagated wave and means for receiving a reflected wave,such as for example antennas 20 and 22, are electrically connected inparallel to the internal feedback means 16. Alternately, the oscillator10 includes an additional or second resonant means 26. The internalfeedback means 1'6 and the external feedback means 18 form a [feedbackmeans on] feedback network 28 capable of producing a feedback signalhaving a phase dependent upon the signals associated with antennas 20and 22.

When the feedback network 28 produces a feedback signal having apredetermined phase, the oscillator 10 produces a radio frequency signalhaving a frequency determined by the resonant frequency of the resonantmeans 14. However, it is not necessary that the oscillator 10 beoperated at the resonant frequency of the resonant means 14. Forexample, the feedback signal from the feedback network 28 may be at aphase other than the predetermined phase which operates the oscillatorat a frequency off the resonant frequency. The radio frequency signal isapplied to one of the antennas, for example antenna 20, and antenna 20radiates the radio frequency signal as a propagated wave. The fieldpattern of the propagated wave is determined by antenna design andenvironmental conditions as known in the art.

A target 30, which is to be detected by the electrical detecting means,intercepts the propagated wave of the radio frequency signal andproduces a reflected wave which is sensed by the other antenna 22. Theantenna 22 upon receiving the reflected wave causes a change in phase ofthe feedback signal from external feedback means 18. The feedback signalfrom external feedback means 18 algebraically adds to the feedbacksignal from the internal feedback means 16 causing a change in phase ofthe feedback signal from the feedback network 28 being applied toamplifier 12 to oscillator 10. Oscillator 10 immediately responds to thefeedback signal change of phase by shifting to a different operatingfrequency. In this embodiment, the oscillator 10 was assumed to beoperating at resonant frequency. Thus, the oscillator operatingfrequency shifts to a frequency off the resonant freq ency. The antenna20 retransmits the new radio freqarncy signal being produced byoscillator 10. Subsequent movement of target 30 changes the reflectedwave being received by antenna 22. The antenna 22 changes the phase ofthe feedback signal from the feedback network 28 causing the oscillator10 to again change its operating frequency.

As the target 30 intercepts the propagated wave, the oscillator changesfrequency as a function of target size and target distance to thereceiving antenna. For example, FIGURE 2 is a graph illustrating awaveform 32 produced by plotting the frequency of the oscillator 10 as afunction of target distance at a right angle, or from the antenna 22.The Doppler frequency of the target produces one cycle of signal as thetarget moves through a distance of /z)\ where is the wavelength of theoscillator frequency. In one experiment, a target moving directly towardthe antenna 22 at a 90 angle and at a rate of 30 cm./sec. produced aDoppler frequency signal of 1.5 cycIes/sec., which signal increased inamplitude as the target moved closer to antenna 22.'

In this embodiment, initially oscillator 10 was'selected to operate at aresonant frequency determined by resonant means 14. This frequency isselected by the feedback network 28 producing a feedback signal having apredetermined phase as described. In FIGURE 2, oscillator 10 in theabsence of target 30 is operating at frequency f,. This is equivalent totarget 30 being at a distance d out of range of the antennas 20 and 22.As target 30 approaches, antenna 22 senses a reflected wave returned bythe intruding target. The antenna 22 changes the phase of the feedbacksignal in the external feedback means 18 and subsequently in thefeedback network 28. When the target 30 reaches a distance d, FIG- URE 2from antenna 22, the frequency of oscillator 10 shifts off of theresonant frequency f to a +Af. As the target 30 moves closer to antenna22, the target passes through several nodes. For example, as the target30 approaches antenna 22, say for example from a distance of 2m to 32m,the frequency of the oscillator shifts to a frequency of Af. As thetarget 30 moves through distances d d, and d the bandwidth or change infrequency of the oscillator increases while cyclically changing from +Afto --Af.

The waveform 32 of FIGURE 2 is plotted by a target 30 moving towardantenna 22 of FIGURE 1 at a uniform velocity. However, if the target 30stops, say for example at point d;,, the frequency of oscillator 10 willstay at the -Af frequency. The Doppler shift frequency would not longerbe generated by oscillator 10 but the fact that the oscillator shiftedoperating frequency from the first frequency f to a second frequencyf-Af indicates detection of a target 30.

The above example assumed that the feedback network 28 produces afeedback signal of a predetermined phase and magnitude which fixed theoscillator 10 frequency at a resonant frequency in the absence of atarget 30. However, the oscillator 10 can be operated off of resonantfrequency in the absence of a target. When a target 30 intercepts thepropagated wave, the oscillator frequency can shift to the resonantfrequency or to another otf resonant frequency. In any event, theoscillator operates at a first frequency determined by a feedback signalat a first phase when the reflected wave is unintercepted and at asecond frequency determined by a feedback signal at a second phase whena target 30 intercepts the propagated wave of radio frequency signal atthe first frequency.

The second resonant means 26 is employed to provide a wide bandimpedance match for the internal feedback means 16, the externalfeedback means 18 and the amplifier l2.

The presence of a target 30, either a moving or a stationary target, isdetectable by measuring the frequency shifts of the oscillator withrespect to time. An output signal is generated by the electricaldetecting means which is the Doppler frequency shift of the oscillator10 as the target 30 moves relative to the antennas 20 and 22 through thenodes illustrated in FIGURE 2.

The Doppler frequency shift (Af is determinable from the followingequation:

where:

Operation of the electrical sensing device requires that the total loopgain of the amplifier, resonant circuit and feedback circuits be greaterthan unity to initiate oscillations. Additionally, the phase shift inthe feedback circuits must be 360 for the embodiment of FIGURE 1 at theoperating frequency. A subsequent change in phase in the feedbackcircuit results in a change of frequency according to the followingequation:

where A=change in phase, Q =loaded Q" of resonant means 14, andf=frequency.

Since the total phase shift in the feedback circuits seeks to stabilizeat 360 after a change in phase represented by ;A, the correspondingchange in the oscillator frequency is determinable per the aboveequation. Further, since the change in oscillator frequency isdeterminable, the change in input power Ap is also readily predictable.Thus, the electrical detecting apparatus operating characteristics canbe monitored either by sensing the Af or Ap of the oscillator 10.

Referring now to FIGURE 3, the graph depicts the response curve of theoscillator 10. The response curve is produced by plotting oscillatorinput power (p) as a function of oscillator frequency (f). When thefeedback network 28 produces a feedback signal having a predeterminedphase, the oscillator 10 produces a radio frequency signal at afrequency determined by the resonant frequency of the resonant means 14.The resonant frequency is depicted on the graph of FIGURE 3 as f, and islocated at the peak power point of the response curve. The input powerto the oscillator 10 at resonant frequency is maximum and is depicted aspoint p, on FIGURE 3.

When a target 30 intercepts the propagated wave and produces a reflectedwave, a feedback signal having a certain phase from external feedbackmeans 18 is superimposed upon the feedback signal having a certain magnitude and phase from internal feedback means 16. Thus, the phase of thefeedback signal from feedback network 28 is an algebraic sum of the twofeedback signals from feedback means 16 and 18. The feedback signal fromfeedback network 28 is applied to the resonant means 26. If the target30 is not an exact integer of AA or wavelengths from the radiating andreceiving means of external feedback means 18 when the reflected wave issensed. the phase of the propagated wave from antenna 20 will bedifferent from the phase of the feedback signal applied to the resonantmeans 14 from the feedback network 28. When this occurs, the oscillator10 changes its operating characteristics to shift its operatingfrequency until the phase of the propagated wave is in phase with thatof the feedback signal from feedback network 28.

As an example, it can be assumed that the oscillator 10 is originallyoperating at resonant frequency determined by the resonant means 14. Theoscillator 10 re sponds to the change of phase of the feedback signal byshifting its frequency of operation to a frequency other that theresonant frequency. The second or new frequency is depicted as point fon the waveform of FIGURE 3. The change of frequency between f, and f,is denoted as Af and the new frequency f, is" off of resonant frequency.Since f is off of resonant frequency, the input power to oscillator 10is immediately decreased as depicted by point p, in the waveform ofFIGURE 2. The change in power of the oscillator 10 between the powerlevel p and p is denoted as Ap.

When a target 30 intercepts the propagated wave estabchange in phase ofthe feedback signal is representative of a target being detected and themagnitude thereof is representative of the magnitude of the phase shift.

The magnitude of the phase shift is a function of several variables suchas the distance between the target and antennas, the integer number ofhalf wavelengths between the target distance and the size of the target.As the target 30 moves through the wave field established by thepropagated wave, the frequency operating point on the graph of FIGURE 3will vary first to one side of the initial frequency, for example topoint f,, then from f, back to f as the target 30 moves closer to theradiating and receiving means of the external feedback means 18 and thento the other side of the graph to a frequency f, and then back againthrough the frequency f,. The discussion of FIGURE 2 indicated that thesweep of frequency as the target moved closer to the antennas not onlyincreased in absolute value butvaried between a Af and a +Af dependingon the integer number of half wavelengths the target 30 is away from theantennas. Thus, a moving target produces discrete values of Af and Ap asillustrated in FIGURE 3 each of which vary in magnitude as a function oftime and the velocity of target 30.

The electrical detecting means of FIGURE 1 can be used in an embodimentwhere the radiation pattern is a closed field. For example, some knownobject such as a wall, a tree or the like can intercept the propagatedwave from antenna 20 and cause a reflected wave to be received byantenna 22 in the absence of a target 30. When a target 30 interceptsthe propagated wave, the antenna 22 detects the presence of target 30 bysensing or detecting a change in phase of the reflected wave. In theabsence of a target 30, the feedback network 28 produces a firstfeedback signal having a phase determined by the reflected wave receivedby antenna 22. An intruding target 80 causes the reflected wave changein phase and thereby changes the phase of the feedback signal from thefeedback network 28 to-the second phase. The change in phase of thefeedback signal from feedback network 28 causes the oscillator to shiftits operating frequency from a first frequency to a second frequency.

The electrical sensing means of FIGURE 1 has utility as a moving objectdetector and the like. For example, an electrical sensing apparatuscould be used as a burglar or intruder sensing device. The apparatuswould be located in a building or area to be secured and connected intoan electrical circuit whereby an alarm would be sounded or some otherindicator actuated when the frequency of the oscillator shiftsindicating that a burglar or some other unauthorized person or objecthas entered the radiation field in the area or building being protected.

Since the Doppler frequency is at a fairly low cycles per second, thisgives the electrical sensing apparatus of the present invention adesirable inherent characteristic. The wavelength of the oscillatorfrequency is such that variations in reflected wave phases due to movingknown objects in a building under surveillance, such as for examplevibrating furnace duct work, metal blinds, slight wall vibration and thelike, will not cause spurious signals.

FIGURE 4 is a schematic diagram of a single transistor circuit which canbe used as an electrical detecting means. In this embodiment, an NPNtransistor 40, connected as common base amplifier, is utilized as theamplifier 12. A voltage dividing network comprising a variable resistor42 and a resistor 44 are connected between a power source 46 which maybe, for example, a negative DC. potential and a ground 48. The base oftransistor 40 is electrically connected to the variable resistor 42 suchthat a preselected bias voltage can be applied between the emitter andbase of transistor 40. The base of transistor 40 is electricallyconnected via a fecdthrough capacitor 50 to ground 48. v

The collector of transistor 40 is electrically connected to the resonantmeans 14. The resonant means 14 includes an inductor 64, formed by athin strip of material formed in a loop, and a variable capacitor 66.

The emitter of transistor 40 is connected to a circuit which forms thesecond resonant means 26. In particular, the emitter of transistor 40 isconnected to a loop inductor 68, which inductor 68 has a variablecapacitor 70 connected between inductor 68 and ground 48 forming theresonant means 26. A resistor 62, electrically connected between thepower source 46 and the inductor 68, establishes the proper bias voltagefor the emitter of transistor 40.

A capacitor is electrically connected between the emitter and collectorof transistor 40 and functions as the internal feedback means 16.Capacitor 60 establishes a first or internal feedback signal fortransistor 40. The transistor 40, resonant means 14 and 26 and capacitor60 form the oscillator generally referred to as oscillator 10 in FIGURE1.

The radiating and receiving means of the external feedback means 18 isformed from a pair of axially aligned dipole antennas 82 and 84. Thefirst dipole antenna 82 is inductively coupled to the resonant means 14by a loop inductor 92 and a variable capacitor 94. The second dipoleantenna 84 is inductively coupled to the resonant means 26 by means ofloop inductor 86 and a variable capacitor 88. The radio frequency signalgenerated by transistor 40 is induced on the antenna 82 via loopinductors 64 and 92 while antenna 84 couples the received signal to thetransistor 40 via loop inductors 68 and 86. A feed-through capacitor 74electrically connects one lead of the inductor 68 to ground 48.

Transistor 40 is driven into oscillation by [a] the internal feedbacksignal which is impressed onto the emitter of transistor 40 by means ofcapacitor 60. The phase of the feedback signal impressed onto transistor40 is preset to a predetermined phase by means of changing the value ofcapacitor 60. In the absence of a target 30 intercepting the propagatedwave being radiated by the antenna 82, the transistor 40 will be driveninto oscillation at a frequency which is equal to the resonant frequencyof inductor 64 and capacitor 66. The signal impressed onto inductor 92is applied to antenna 82. Antenna 82 radiates the radio frequency signalin a propagated wave, which in this embodiment, is a continuous wave.Thus, antenna 82 radiates a radiation field of radio frequency signalsat a first frequency which is determined by the first phase of thefeedback signal.

When a target 30 intercepts the radiated propagated wave from antenna82, the target 30 reflects the intercepted wave back to the antenna 84.The signal sensed by antenna 84 is applied as a radio frequency signalvoltage, the magnitude of which is determined by the reflected wave,across loop inductor 86 and capacitor 88. The radio frequency voltageimpressed across the series connected inductors and capacitor of antenna84 produces [a] an external feedback signal which is coupled to theemitter of transistor 40 via inductor 68. The [resulting] resultantfeedback signal impressed onto the emitter of transistor 40 is acombination of the feedback signals produced from the capacitor 60 andthe antenna 84 and is changing in phase as a function of the targetsreflected waves. A resultant feedback signal having a new phase causesthe transistor 40 to shift its operating frequency to a second frequencywhich is determined by the phase of the feedback signal. The radiofrequency signal having a frequency which is equal to the secondfrequency is then induced onto the antenna 82 by means of an inductivecoupling between inductors 64 and 92. Antenna 82 the rn' radiates theradio frequency signal at the second frequency in the form of apropagated wave.

Phase correction of the feedback signal at the emitter of transistor 40is obtained by shifting the operating frequency to a frequency where theresultant phase of the feedback signal is made equal to the phase of thefeedback signal before target 30 intercepts the propagated wave.

As the target 30 changes position. the antenna 84 produces a feedbacksignal having a different phase which will then be superimposed onto thefeedback signal from capacitor 60 to again change the frequency ofoperation of transistor 40. In this-embodiment, as target 30 movesrelative to antennas 82 and 84, the change of phase of the feedbacksignal supplied via antenna 84, inductors 86 and 68 to the emitter oftransistor 40 is time related.

An output signal from the electrical detecting means can be obtained byconnecting an output terminal 98 between the resistor 62 andfeed-through capacitor 74. The frequency of the output signal plotted asa function of distance is a sine wave which is the Doppler function oftarget velocity. Both the oscillator operating frequency and the inputpower thereto changes as a function of the detected target rate ofmovement.

In one embodiment of FIG. 4, the following components were utilized:

Component: Value Tansistor 40 RCA40235. Resistor 42 50009. Resistor 4440000. Power source 46 10 V. DC. Resistor 62 2700. Capacitors 50, 741500 pf. Capacitors 66, 70, 88, 94- .24.5 t. Capacitor 60 1 pf.(intrinsic). Inductors 64, 68 /fi turn of silver strip .75" x .125" x.007. Inductors 86, 92 Straight silver strip .50 x .125" x .007"Antennas 82, 84 4"-- 14 gauge silve r wire.

Characteristics Frenquency range .55-1 gHz. Radiated power 50-100 w.Coverage 50 foot circle.

FIGURE 5.is a schematic diagram of another embodiment of an electricaldetecing apparatus wherein a single NPN transistor 100 is utilized asthe amplifier 12, which transistor 100 is connected in a common emitterconfiguration. The circuit of FIGURE differs from that of FIGURE 4 inthat the receiving antenna, designated as 108, is directly connected tothe transistor 100 via variable coupling capacitor 110. A variablecapacitor 112 and inductor 109 function as the internal feedback meansfor establishing the internal feedback portion of the feedback signal.Inductor 114 is a radio frequency choke used for isolating the base leadof transistor 100 from ground.

FIGURE 6 is yet another embodiment of an electrical detecting means ofthis invention. The circuit of FIG- URE 6 dilfers from the circuits ofFIGURES 4 and 5 in that both antennas 120 and 122 are directly connectedvia capacitors 124 and 126 respectively to an NPN transistor 128connected in a common base configuration.

FIGURE 6 also includes therein an output sampling means 132 which isconnected to the frequency producing means or oscillator which includesthe transistor 128. The oscillator is periodically disabled by theoutput sampling means 132 for a predetermined time interval determinedby the producing means. The output sampling means 132 converts the sinewave, which varies in frequency as a Doppler function of targetvelocity, into an output signal appearing on an output terminal 134having pulse period modulation. This enables the electrical detectingmeans to operate as before, except that the power requirements of thepower source can be substantially reduced. The output sampling means 132includes a capacitor 138, a capacitor 140 and resistors 142 and 144.Capacitor 138 is operatively connected between ground and the emitter oftransistor 128. A resistor-capacitor charging circuit comprisingcapacitor 138 and resistor 142 produces an output signal at terminalpoint "a." A plot of the voltage versus time of the output signal atterminalpoint a" is illustrated as the waveform in the graph of FIGURE7A. Capacitor 140 and resistor 144 receive and differentiate thewaveform illustrated in FIGURE 7A producing an output signal havingpulse period modulation. A plot of the differentiated output signalappearing at output terminal 134 is a waveform illustrated in the graphof FIGURE 73.

The antenna 122 radiates the radio frequency signal at a frequencydetermined by the operation of the oscillator. Thus, by means of aremote receiver 146, the radiated radio frequency signal can be sensedwithout a physical connection to the device. When a target interceptsthe propagated wave from the antenna 122 and produces a reflected wave,the output signal from the output sampling means 132 and the radiofrequency signal received by the remote receiver 146 concurrently eitherincrease or decrease as a function of target movemenhA change of pulserate when detected by the remote receiver 146 indicates a moving target30 intercepting the propagated radio frequency signal radiated byantenna 122.

The pulse period modulation output signal from the output sampling means132 or the demodulated signal from the remote receiver 146 can beprocessed through a double integrator circuit to recover the sine wavewhich is a direct function of the Doppler frequency shift attributed tothe target 30.

The electrical detecting means of the present invention can be adaptedas a pulse controlled radar system for detecting the range, velocity anddirection of a moving target.

One embodiment of such a pulse controlled radar system is illustrated inFIGURE 8. The radar system includes an oscillator 148 which includes anamplifier 150. a resonant frequency circuit 152 and a feedback circuit154. The oscillator 148 produces a radio frequency signal at theresonant frequency of circuit 152 when a feedback signal is appliedthereto having a predetermined phase. The oscillator 148 produces aradio frequency signal at a frequency which is off the resonantfrequency when the feedback signal being applied thereto has a timerelated phase shift wherein the particular phase of the feedback signalis at a phase other than the predetermined phase.

166 is adapted to have two positions which are sequenced automatically.When switch 166 is in its first or transmit position, an amplified radiofrequency signal pulse from amplifier 156 is passed to antenna 164whereupon the amplified radio frequency signal pulse is radiated in apropagated wave. Immediately after the antenna 164 transmits a pulse,the antenna switch 166 automatically transfers to its second or receiveposition. In the event a target 30 intercepts the transmitted radiofrequency pulse, a refiected radio frequency signal pulse will bereturned and sensed by the antenna 164. The antenna switch 166automatically returns back to its first or transmit position insuflicient time to transmit a subsequent radio frequency pulse.

When the antenna switch 166 is in its second or receive position, theradar system can receive a reflected pulse of radio frequency signalindicating a target. When a moving target intercepts a radio frequencysignal pulse transmitted by the antenna 164, a reflected pulse isreturned by the 1 1 target to the antenna 164. The antenna 164 appliesthe received pulse to the oscillator 148 via antenna switch 166 andamplifier 172 to a second feedback circuit 170.

The second feedback circuit 170 produces a second or external feedbacksignal whichis amplified by amplifier 172 and superimposed on the firstfeedback signal produced by the internal feedback circuit 154. Theresultant feedback signal having a phase determined by the algebraic sumof the two feedback signals, is applied to oscillator 148 causing theoscillator to change operating frequency and input power as a functionof a detected moving target.

An output sampling means 176 is adapted to be connected to theoscillator 148 for converting the shifts in oscillator operatingfrequency at into target velocity. The output sampling means 176 iscapable of converting the time interval between the time a radiofrequency signal pulse was transmitted by the antenna 164 and the timethe antenna 164 received a target reflected radio frequency pulse intotarget range and direction, the direction being determined from thedirection of the rotatable directional antenna. The parameters of' thedetected target, such as the range, velocity and direction, are producedas an electrical signal on output 178.

The signal appearing at output 178 is in the form of a pulse trainvarying wherein the pulses having uniform time duration vary infrequency and in time intervals therebetween. The graph of FIGURE 9depicts a waveform of the output signal. The waveform is produced byplotting the frequency (f) as a function of time (t). The uniform timeduration of each pulse is determined by the control pulses applied toamplifier 156 from the pulse source via pulse input 158.

Referring to the waveform of FIGURE 9, frequency of oscillator 148 isdenoted as f on one output pulse 182. The change in frequency at of thepulses represents target velocity.

The interval between pulses, such as for example the time intervalbetween the leading edges of pulses 186 and 188, is represented by t,..The time interval t is used to represent target range or distance. Thedirection of target movement is a function of the angular rotation 6 ofantenna 164 and the A9 between pulses is used for target direction. p

The above embodiments of the electrical detecting means of thisinvention are not intended to limit the scope of the present invention.It is contemplated that any and all modifications, uses, equivalents andthe like are within the scope of the appended claims.

What is claimed is:

1. Electrical detecting means comprising:

means including resonant means for producing a radio frequency signal ata resonant frequency in response to a feedback signal having apredetermined phase and for producing said radio frequency signal at afrequency off said resonant frequency when said feedback signal has aphase other than said predetermined phase; means for radiating saidradio frequency signal in a propagated wave and for receiving areflectedwave when a target intercepts said propagated wave; and feedback meansoperatively connected to said producing means and said receiving meansfor establishing said feedback signal having a frequency which isdetermined by the frequency of said producing means at a first phase tooperate said producing means at a first frequency when said propagatedwave is unintercepted by said target and for changing the phase of saidfeedback signal to a phase other than said first phase to shift thefrequency of said producing means and said feedback signal from saidfirst frequency to a second frequency in response to said receivingmeans detecting a reflected wave from said target intercepting saidpropagated wave.

2. The electrical detecting means of claim 1 wherein:

said [means for radiating said radio frequency signal in a] propagatedwave is intercepted by a known object and a reflected wave from thisobject is received by said receiving means whereby a radiation patternin the absense of a target is established, said receiving means beingresponsive to a target intercepting said radiation pattern by detectinga change in phase of said reflected wave, said feedback means beingresponsive to said receiving means detecting said pha'se change to shiftthe frequency of said producing means from said first frequencyestablished by a feedback signal in the absence of said target but inthe presence of said object to a second frequency in response to saidreceiving means detecting said phase change when said target interceptssaid radiation pattern.

3. The electrical detecting means of claim 1 wherein said resonant meansis a resonant circuit and said feedback signal first phase is saidpredetermined phase whereby said producing means produces a radiofrequency signal at a frequency determined by the resonant frequency ofsaid circuit and said producing means shifts to a frequency off saidresonant frequency when said feedback signal is shifted to a phase otherthan said first phase.

4. The electrical detecting means of claim 1 further including:

output sampling means connected to said producing means for passing asan output signal a sine wave which varies in frequency as a Dopplerfunction of target velocity and which is generated by said producingmeans shifting frequency as said receiving means receives reflectedwaves from said target.

5. The electrical detecting means of claim 1 further including:

output sampling means operatively connected to said producing means fordisabling said producing means operation in predetermined time intervalsdetermined by said producing means for converting a sine wave whichvaries in frequency as a Doppler function of target velocity into anoutput signal having pulse period modulation.

6. An electrical detecting apparatus comprising:

an oscillator including a resonant frequency circuit for producing aradio frequency signal at the resonant frequency of said circuit inresponse to a resultant feedback signal having a predetermined phase,said oscillator producing said radio frequency signal at a frequency offsaid resonant frequency when said resultant feedback signal has a phaseother than said predetermined phase; first antenna adapted to beoperatively coupled to said oscillator for radiating said radiofrequency signal in a propagated wave; second antenna adapted to beoperatively coupled to said oscillator for receiving a reflected wavereturned by a target intercepting said propagated wave and] and forproducing an external feedback signal in response to said reflectedwave; and [a feedback network connected between said oscillator and saidfirst and second antennas for establishing said feedback signal at afrequency substantially equal to the frequency of said oscillator, said'feedback network including means for establishing a first feedbacksignal having a first phase to operate said oscillator at a firstfrequency and means for establishing a second feedback signal inresponse to said second antenna detecting a reflected wave, said sec-'ond antenna upon detecting a reflected wave from said target beingresponsive to a change in phase of said second feedback signal as afunction of the change in phase of said reflected wave as said targetmoves relative to said second antenna, said second feedback signal beingsuperimposed on said first feedback signal to apply to said oscillator afeedback signal having] internal feedback means in said oscillatorincluding means for establishing an internal feedback signal andincluding means for a first feedback circuit connected in parallelrelationship superimposing said external feedback signal on saidinternal feedback signal to form said resultant feedback signal, whichresultant feedback signal has a changing phase for shifting theoperating frequency of said oscillator as said target moves relative tosaid second antenna, said shift in oscillator frequency to saidoscillator for establishing a first feedback signal having a first phaseto operate said oscillator at a first frequency;

a pulse controlled amplifier operatively connected to receive acontinuous radio frequency signal from said oscillator for producingpulses of radio frequency signal-having ap redetermined duration, saidamplifier being adapted to be operated in response to control pulsesfrom a pulse source;

a rotatable directional antenna adapted to be operably connected to saidamplifier for radiating said pulses in a propagated wave and receivingreflected pulses of radio frequency signal returned by a targetintercepting said propagated wave of detecting pulses;

a second feedback circuit capable of producing a second first and secondantennas and the remainder of said feedback network for adjusting eachantenna impedance.

ing a propagated wave of radio frequency signal into space and forreceiving a reflected wave when said propagated wave ,is intercepted inspace by a target, said external feedback means being electricallyconfeedback signal and adapted to be connected between said antenna andsaid oscillator, said second feedback circuit including a radiofrequency signal amplifier for amplifying reflected pulses received bysaid an- 10. The apparatus of claim 6 further includin I an outputsignal sampling device connected to said. tenna target mmceptmg saiddFtectmg Rulses oscillator for disabling said oscillator forpredeterproducmg F feedback gg a mined time intervals determined by saidproducing {elated phasehsmd second fcedtiack 818ml i means forconverting said sine wave which varies F on sand. first fFedback signaland aPphed in frequency as a Doppler function of Ears vel'ociy to saidoscillator, satd oscillator being responsive to into an output signalhaving lse cried modu: said time related phase to shift from said firstfrelation p p quency to a second frequency; 1 d

an antenna switching means operative y connecte to grg f i f detectingapparatus of claim fursaid antenna and adapted to connected separately aremote receiver tuned to the operating frequency of to said p-ulseconm'med ar'nphfier and s'aldhlradlo he. said oscillator for receivinthe ro a ated ad'o quFncy slgnalamphficr-sald amcnna swltc mg meansfrequency signal havin fliSC riofi modulirtitin being aimed-ed to sa'ldpulse contained amphfier when, said t 3 p be d for passing 581ddetecting pulses to said antenna for a P 'ontcan momlore the duration ofeach detectlng pulse, said antenna 1,"r:szssszszassz:s

i td lse to sai am i er urin em ermeans including resonant circuit meanscapable of prO- 1:5 a izgg gg Dukes; id 8 ducmg a frsquqncy s'gnal atthe resonant output sampling means adapted to be connected across quencyof said CllC lIlt and at a frequency o fi aid oscillator for convertingthe oscillator frequency i frequency m response to a change of 513ml 40shift between said first frequency andsatd second freint}: 33} dback e IHi 11 t d t quency into target velocity, the time mterval between eam.ans e ec Y come: e 0 the time said antenna transmits a detecting pulseand :21 frilqucncy slgnal profiucmg mFanS for anal" the time a reflectedpulse is detected by said antenna z g gg of sad Producmg means at a intotarget range, and targetddtrecnor;J l1s rgrterrnmed r direction of sairotata e rrecttona external feedback means including means for radiat-333 2 14. An electrical detecting means for sensing the presence of atarget in a predetermined area comprising:

means for producing a radio signal at a frequency at which maximumenergy is transmitted tn response to nected in parallel relationshipwith said internal feeda sultan, feedback i l h i a redetermined backmeans and adapted to produce a change of phase phase and for [producing]h i h frequency of signal across said mternal feedback means in r i d disignal [at a first] t a frequency [off the] Spouse to a change [ofPhase] in difierence other than the frequency of maximum energy transfertween the Phase of a reflected wave and the Phase [frequency]when theresultant feedback signal has of the propagated wave, said internalfeedback means a phasc other than said predetcrmimd h bemg resPonslye tosaid external fefidback, means means operatively coupled to saidproducing means for flpplymg f of to and 9 radiating [a] said radiosignal [at a first frequency] radio frequency signal producing meanscausing san in a prOgagated wave into said predetermined area; [oscmamr]radio frequency signal producing mean internal feedback meansoperatively connected with to change from Sam first q i second saidradiating means, for producing a first feedback quency whereby targetdetectlonns rndtcated by the signal shifted in [having a] phase from thephase frequency dlference between Sald first and second [whichestablished the frequency] of said radio sigfrequency. l MI I; and

A pulie controlled f System detecung the means including receiving meansoperatively connected "9? veloclty and dlrecuon of a movmg target tosaid internal feedback means for receiving a repnsmg flected wave ofsaid propagated wave returned by said an oscillator includ ng a resonantfrequency circuit for target and for providing a phase changing feedbackProducm? a raflm frcquencli f j at a resonant signal in response to saidreflected wave and superimfmquency P 531d "E c'rclm response posing saidphase changing signal on said first feedfudback slgnal havmg PredcmrmlmdP 531d back signal tojnrm said resultant feedback signal oscillatorproducing said radio frequency signal at :1 [produced by a f dba kmeans,

fmqllflflcy said n t frequqncy in p said feedback means responding tosaid phase changing Said fccdback signal B M81! Phasc signal receivedfrom said receiving means for prowherein the phase thereof is at otherthan said pre-4 ducing a feedback signal having a frequencydeterdetermined phase; mined by said producing means] for shifting thefre- 15 16 quency of said producing means to a frequency other I theradio frequency oscillator to cause the frequency than said firstfrequency in response to a change in of the propagated wave to vary whena moving obphase of said reflected wave. iect is intercepting thepropagated wave. 15. The electrical detecting means of claim 14 furthercomprising: 5 7 References Cited means operatively l Sal}! Producmgmeans The following references, cited by the Examiner, are f E salddeviations} q y P of record in the patented file of this patent or theoriginal vlding an output signal WhlCll vanes in proportion to patentsaid frequency deviations. UNITED STATES PATENTS I 6. Electricaldetecting apparatus comprising: j

a feedback oscillator for producing a radio frequency 4 gfii yz a 2 7signal;

means for radiating the tradio frequency signal in a pr0- 532;:

pagated wave; and

means for receiving a reflected wave of the radio frequency signal whenan object intercepts the propa- RODNEY D BENNETT JR primarygsxamimrgated wave and for applying an electrical signal representative of thereflected wave to the oscilaltor H-TUBBESING, Assistant fl in l'feedback path whereby a change in the phase of the signal representativeof the reflected wave produces 20 a corresponding change in thefrequency of the pro- 343 7'7i 340-458 pagated wave of radio freqencysignal produced by 3,289,204 11/1966 Murray et al. 3437.5

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. Reissue2706 Dated February 16, 1.971

lnventofl s) Lincoln H. Chariot, Jr.

It.-;Is 'certified. that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

I Col. 3, line 3, change the work "bulkyl to bulky Col. 5', line 2%,chenge "32:1 to 3/2n .061. 5, line 3 1 change "not" to no ---3 Col. 8,line 71, change "themf to then --5 Col. 9, line 42, change "detecting"to detecting col. 10, line 37, change '5" to Col. 13, line 10, change"retecttng" to detecting Col. 14; line 8;, change ap' redetermined" to apredetermined Signed and sealed this 10th day of August 1971.

(SEAL) Attest:

' EDWARD H.FLEI'GHER,JR. WILLIAM E. SCHUYLER, JR.

Atteating Officer Commissioner of Patents

